Activation of brain somatostatin 2 receptors stimulates feeding in mice: analysis of food intake microstructure.

We recently reported that the oligosomatostatin receptor agonist, ODT8-SST increases food intake in rats via the somatostatin 2 receptor (sst(2)). We characterized ingestive behavior following intracerebroventricular (icv) injection of a selective sst(2) agonist in freely fed mice during the light phase. The sst(2) agonist (0.01, 0.03, 0.1, 0.3 or 1μg/mouse) injected icv under short inhalation anesthesia dose-dependently increased cumulative light phase food intake over 4h compared to vehicle with a 3.1-times increase at 1μg/mouse (p<0.05). Likewise, the sst(2,3,5) agonist octreotide (0.3 or 1μg/mouse) dose-dependently increased 4-h food intake, whereas selective sst(1) or sst(4) agonists at 1μg/mouse did not. In vehicle-treated mice, high fat diet increased caloric intake/4h by 2.8-times compared to regular diet (p<0.05) and values were further increased 1.4-times/4h by the sst(2) agonist. Automated continuous assessment of food intake established a 6.6-times higher food intake during the dark phase due to increased number of meals, meal size, meal duration and rate of ingestion compared to non-treated mice during the light phase. During the first 4h post icv sst(2) agonist injection, mice had a 57% increase in number of meals with a 60% higher rate of ingestion, and a 61% reduction in inter-meal intervals, whereas meal sizes were not altered compared to vehicle. These data indicate that the activation of brain sst(2) receptors potently stimulates the light phase ingestive behavior under basal or high fat diet-stimulated conditions in mice. The shortened inter-meal interval suggests an inhibitory effect of the sst(2) agonist on "satiety", whereas "satiation" is not altered as indicated by normal meal size.